Optical: Numerical determination of the flow curves of anisotropic steels and failure prediction

A combined experimental - numerical method is presented here for the stress-strain characterization of ductile anisotropic metals. The experimental side of the method is based on the simultaneous video acquisition of tensile round bars from two different angles, for determining the true stress-true strain curves of highly anisotropic ductile metals. Then the material-independent MLR correction, derived in previous works from numerical simulations of tensile tests with many different metals, is applied to the experimental true stress-true strain curve, so obtaining an accurate post-necking flow curve of the material. The proposed procedure is applied to tensile specimens of an X100 steel for piping, machined with different notches along different orientations within a rolled plate cut from a large size pipe. The flow curves and the Hill parameters identifying the behavior of the X100 steel are derived by applying the proposed procedure to the tests of smooth specimens alone; the experiments with notched specimens are then simulated by finite elements, using as input the material data from smooth bars. The experimental - numerical comparison evidences the accuracy of the whole material data used and, in turn, the suitability of the proposed procedure. Finally, the Bao-Wierzbicki damage model is implemented in a subroutine ran together with a new series of FE analyses, obtaining failure predictions very close to experiments